eprintid: 1472616 rev_number: 24 eprint_status: archive userid: 608 dir: disk0/01/47/26/16 datestamp: 2015-11-16 14:38:25 lastmod: 2021-09-26 22:53:21 status_changed: 2015-11-16 14:38:25 type: article metadata_visibility: show creators_name: Deller, A creators_name: Cooper, BS creators_name: Wall, TE creators_name: Cassidy, DB title: Positronium emission from mesoporous silica studied by laser-enhanced time-of-flight spectroscopy ispublished: pub divisions: UCL divisions: B04 divisions: C06 divisions: F60 keywords: antimatter, positronium, diffusion, tunnelling, mesoporous silica note: Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. abstract: The use of mesoporous silica films for the production and study of positronium (Ps) atoms has become increasingly important in recent years, providing a robust source of free Ps in vacuum that may be used for a wide variety of experiments, including precision spectroscopy and the production of antihydrogen. The ability of mesoporous materials to cool and confine Ps has also been utilized to conduct measurements of Ps–Ps scattering and Ps2 molecule formation, and this approach offers the possibility of making a sufficiently dense and cold Ps ensemble to realize a Ps Bose–Einstein condensate. As a result there is great interest in studying the dynamics of Ps atoms inside such mesoporous structures, and how their morphology affects Ps cooling, diffusion and emission into vacuum. It is now well established that Ps atoms are initially created in the bulk of such materials and are subsequently ejected into the internal voids with energies of the order of 1 eV, whereupon they rapidly cool via hundreds of thousands of wall collisions. This process can lead to thermalisation to the ambient sample temperature, but will be arrested when the Ps deBroglie wavelength approaches the size of the confining mesopores. At this point diffusion through the pore network can only proceed via tunneling, at a much slower rate. An important question then becomes, how long does it take for the Ps atoms to cool and escape into vacuum? In a direct measurement of this process, conducted using laser-enhanced positronium time-of-flight spectroscopy, we show that cooling to the quantum confinement regime in a film with approximately 5 nm diameter pores is nearly complete within 5 ns, and that emission into vacuum takes ~10 ns when the incident positron beam energy is 5 keV. The observed dependence of the Ps emission time on the positron implantation energy supports the idea that quantum confined Ps does not sample all of the available pore volume, but rather is limited to a subset of the mesoporous network. date: 2015-04-28 date_type: published official_url: http://dx.doi.org/10.1088/1367-2630/17/4/043059 oa_status: green full_text_type: pub language: eng primo: open primo_central: open_green verified: verified_manual elements_id: 1034586 doi: 10.1088/1367-2630/17/4/043059 lyricists_name: Cassidy, David lyricists_name: Deller, Adam lyricists_id: DBCAS57 lyricists_id: AMDEL12 actors_name: Deller, Adam actors_name: Barczynska, Patrycja actors_id: AMDEL12 actors_id: PBARC91 actors_role: owner actors_role: impersonator full_text_status: public publication: New Journal of Physics volume: 17 article_number: 043059 issn: 1367-2630 citation: Deller, A; Cooper, BS; Wall, TE; Cassidy, DB; (2015) Positronium emission from mesoporous silica studied by laser-enhanced time-of-flight spectroscopy. New Journal of Physics , 17 , Article 043059. 10.1088/1367-2630/17/4/043059 <https://doi.org/10.1088/1367-2630%2F17%2F4%2F043059>. Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/1472616/1/document.pdf